Curved, bent, offset, non-traditional seat tube

I must say that my nuts appreciate these curved, bent, offset, non-traditional seat tubes. I've clipped them enough on the back of the saddle, even with it dropped a bit. I notice with curved seat tubes, dropping the saddle out of the way pushes it forward and the amount of room you gain to use your legs and hips feels luxurious over standard bikes. It's like what bent/curved top tubes did for standover height and curved stays did for heal clearance. I wish more bike makers did this! I've already crossed off a few bikes off the "interested in" list that didn't have this. That and I'm a big 29er fan, and just discovered what a 16.5" chainstay (44.5" wheelbase) bike can do to refresh the experience of trails I've ridden for years.

Why isn't this more common? I don't know the downsides, but if they aren't major, I wouldn't mind see it on more frames.